Narrative:

[We] encountered unforecast weather en route. Under night vision goggles (nvg); clouds appeared to be forming near our altitude; but not along our flight path. [I] momentarily flipped up goggles to help in determining if weather conditions were in fact deteriorating along our route. Visibility appeared to be less than forecast; but acceptable; and within minimums. Flipped goggles down; area at 12 o'clock started to appear undefined; but I could still see light sources at 5 miles and beyond; and I could see the horizon. [I] then entered IMC conditions; climbed to MSA; contacted ATC; declared emergency; and asked for vectors to ILS at ZZZ. Just about the same time as being established on the localizer; broke out into VMC. Continued on approach for a few minutes to verify weather conditions warranted canceling IFR clearance. Canceled and returned to base in VMC without further incident. Reported ceilings were ovc 39; forecast conditions were sct 20; broken 40. [I] entered IMC at approximately 2;700 MSL or 2;200 AGL. Crew did an excellent job assisting with approach plate and keeping sterile cockpit. Total time in IMC was about 10 minutes. I executed the recovery procedure as directed in the [operating manual]. Prior IFR experience helped me to stay calm; but was in no way a factor which caused us to continue flight in deteriorating conditions. Entering the clouds was a surprise. I did not feel prior to entering IMC that I should turn around. There simply were not adequate warning signs. Low experience level with nvg may have been a factor in not being able to accurately determine the base of the unforecast cloud layer.

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Original NASA ASRS Text

Title: BK-117 pilot inadvertantly entered IMC; declared an emergency; received vectors for an ILS approach and; once established on the approach entered VFR conditions and returned to base. Pilot believes that low experience level with Night Vision Googles may have been a factor.

Narrative: [We] encountered unforecast weather en route. Under Night Vision Goggles (NVG); clouds appeared to be forming near our altitude; but not along our flight path. [I] momentarily flipped up goggles to help in determining if weather conditions were in fact deteriorating along our route. Visibility appeared to be less than forecast; but acceptable; and within minimums. Flipped goggles down; area at 12 o'clock started to appear undefined; but I could still see light sources at 5 miles and beyond; and I could see the horizon. [I] then entered IMC conditions; climbed to MSA; contacted ATC; declared emergency; and asked for vectors to ILS at ZZZ. Just about the same time as being established on the localizer; broke out into VMC. Continued on approach for a few minutes to verify weather conditions warranted canceling IFR clearance. Canceled and returned to base in VMC without further incident. Reported ceilings were OVC 39; forecast conditions were SCT 20; BKN 40. [I] entered IMC at approximately 2;700 MSL or 2;200 AGL. Crew did an excellent job assisting with approach plate and keeping sterile cockpit. Total time in IMC was about 10 minutes. I executed the recovery procedure as directed in the [Operating Manual]. Prior IFR experience helped me to stay calm; but was in no way a factor which caused us to continue flight in deteriorating conditions. Entering the clouds was a surprise. I did not feel prior to entering IMC that I should turn around. There simply were not adequate warning signs. Low experience level with NVG may have been a factor in not being able to accurately determine the base of the unforecast cloud layer.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.